Commercially available mouth guards are pre-fitted, and come in standardized shapes and sizes. Professional athletes participating in contact sports such as football routinely wear custom fitted mouth guards, and they have a relatively lower incidence rate of dental injuries. However, in other sports such as basketball, the wearing of mouth guards is not widely practiced, and the incidence rate is much higher, with 34 percent of all basketball injuries falling into the category of dental injuries. One of the reasons of poor compliance with mouth guard protection is that many commercially available mouth guards are uncomfortable to wear. They tend to be bulky, making it difficult to talk and breath while participating in sports activities.
Dental injuries, including fracture and loss of teeth, are the most common orofacial injuries occurring in many sports despite the use of commercially available mouth guards. This indicates insufficient protection from currently used products. An ideal mouth guard would have excellent fit and retention, must be comfortable to wear, allow the wearer to speak and breathe without hindrance, but be tear resistant, resilient, and protective.
The term “mouth guard” refers to a wide range of products. The American Society for Testing and Materials has issued ASTM Designation: F697-80, (1992), providing a standard practice for care and use of mouth guards. ASTM has classified mouth guards into stock mouth guards, mouth-formed mouth guards, and custom-fabricated mouth guards.
Approximately 90 percent of mouth guards are sold in sporting goods stores. The least expensive and also least effective type of mouth guard is the stock mouth guard. These mouth guards come in limited sizes, and lack retention. To be held in place, the wearer must constantly bit down on them. These types of mouth guards hinder verbal communication and interfere with breathing, and tend to be uncomfortable and bulky. Often, users cut them to make them more comfortable, but this reduces the protective function.
The second type of mouth guard falls into the category of “boil & bite” mouth guards. These are the most widely used mouth guards. They contain a thermoplastic material, almost exclusively ethyl vinyl acetate (EVA) that can be softened by immersion into boiling water, and then formed by pressing the softened material over the teeth with fingers, followed by biting down on the softened material until it hardens while it cools down. There has been some concern voiced by dentists that these types of mouth guards often lack proper extensions and fail to cover all the posterior teeth. As with stock mouth guards, athletes are tempted to cut and reshape these mouth guards in attempts to make them more comfortable, as they have poor fit, limited retention, and in some cases trigger the gag reflex. According to Dr. Joon Park (First International Symposium on Biomaterials, August 1993) boil and bite mouth guards suffer a drastic decrease in occlusal thickness during the molding process, eliminating a significant portion of the protective properties of the mouth guard and giving the wearer a false sense of protection.
Only about 10 percent of all mouth guards in use today are custom fitted by dental professionals. For so-called vacuum mouth guards, the dentist first takes an impression of the patient's teeth, and a stone cast of the maxillary, upper, arch is fabricated. Then, a thermoplastic material, usually a polyethylene vinyl acetate copolymer (EVA) is molded over the stone cast while applying a vacuum. The resulting mouth guard is then trimmed and polished. Alternatively, multiple layers of polymer are laminated together under pressure in an attempt to improve the physical properties of the protective layers.
These custom-made mouth guards tend to be very expensive, and require a visit to the dentist, and, in some cases, fabrication in a dental laboratory. The expense and complexity of getting a custom fitted mouth guard has hindered customer acceptance, and most custom fitted mouth guards are purchased by professional athletes, but have not penetrated the general consumer market. In an experimental series at University of Michigan Dental School, acrylic resins have been used to increase the tensile strength for mouth guards for ice hockey players. Protection for significant impact, e.g. from a direct hit of a hockey puck or hockey stick, has increased, but the prize for these mouth guards is significantly higher than for a regular EVA based custom made mouth guard, and the mouth guard got significantly thicker and therefore uncomfortable. However, the principle of using a hard material, e.g. acrylic resins, in contrast to a soft material, e.g. EVA, appeared to be better from a teeth protective standpoint.
Typical impact energy absorbing a materials used for protective athletic gear are open or closed cell foams of various thermoplastic polymers including polyurethane, polyethylene, polystyrene, as well as foams or dense bodies of elastomeric polymers, including silicones, ethylene vinyl acetate (EVA), ethylene-propylene rubbers (EPM), ethylene-propylene-diene rubbers (EPDM). In addition to single component materials, various composite materials have been reported. Many of these materials contain mixtures of polyethylene with fibers (U.S. Pat. No. 4,946,721, issued Aug. 7, 1990). Other approaches include composites of rigid hollow spheres encapsulated in an elastomeric matrix (U.S. Pat. No. 4,101,704, issued Jul. 18, 1978), or composites of elastomers with fillers (U.S. Pat. No. 4,082,888, issued Apr. 4, 1978).
There have also been attempts to improve the impact energy absorption capacity of materials by laminating different layers together. For example, European Patent EP 0 955 211 B1, issued Jan. 28, 2004, teaches impact energy absorbing materials for protective athletic gear, including mouth guards, using layers of expanded polytetrafluoroethylene (ePTFE) and at least one layer of an elastomer.
U.S. Pat. No. 5,051,476 (Sep. 24, 1991) resides in an improved mouth guard composition comprising and ethylene/vinyl acetate copolymer with 4-50 percent of a thermoplastic polycaprolactone, optionally with polyvinyl acetate, colorants, and perfumes. However, due to the large EVA content, these mouth guards do not take full advantage of the superior materials properties of polycaprolactone.
Polycaprolactone mixed with a thermoplastic rubber material has a softening point of 50-70° C., and has been used as orthopedic splinting or casting material (U.S. Pat. No. 4,661,535, Micale J. Borroff, Donald A. Willstead, Apr. 28, 1987). The filler added to polycaprolactone can also be a mixture of talc, and calcium silicate.
Polycaprolactone has also been used as scaffolding material for bone tissue engineering (Jessica M. Williams, Adebisi Adewunmi, Rachel M. Schek, Colleen L. Flanagan, Paul H. Krebsbach, Stephen E. Feinberg, Scott J. Hollister, and Suman Das, “Bone tissue engineering using polycaprolactone scaffolds fabricated via selective laser sintering”, Biomaterials 26 (2005) 4817-4827). The solid free form fabrication technique employed allows precise control over pore size, permeability, and stiffness.
U.S. Pat. No. 5,339,832 discloses a thermoplastic boil & bite type mouth guard that has an integrated shock absorbing framework. This mouth guard is a composite made from a thermoplastic material and a low compression elastomer framework embedded in the U-shaped portion of the mouth guard. The shock-absorbing insert is intended to attenuate and dissipate forces acting on the mouth guard.
In U.S. Pat. No. 5,293,880, an athletic mouth guard is reported that is based on a unitary structure comprising a mouthpiece and an elongated strap adapted for attachment to face masks of helmets. The mouthpiece has walls of different thicknesses in different regions so that the forces of an upwardly directed blow are transmitted more to the posterior teeth than the anterior teeth.
U.S. Pat. No. 5,746,221, issued May 5, 1998, relates to a cold-formable thermoplastic mouth guard material that has a very low softening point, making it possible for the user to custom-fit the mouth guard without requiring the services of a dentist. The mouth guard comprises a U-shaped structure comprising an expanded PTFE material that can be shaped at room temperature. The patent also discloses one coating on at least a portion of the surface of the mouth guard. The user places the mouth guard into the mouth and bites down to retain the contours of the teeth. The mouth guard's energy absorption capacity has been tested according to ASTM D1054-91, Standard Test for Rubber Property Resilience Using a Rebound Pendulum. These tests indicate that the expanded PTFE materials absorb about 75 percent of the impact energy, while conventional mouth guards absorb only about 50-65 percent of the energy. This patent also mentions the use of one or more fillers, in direct reference to U.S. Pat. No. 4,985,296 that teaches the formation of expanded PTFE materials with fillers incorporated therein.
U.S. Pat. No. 5,746,221 teaches the use of fillers to enhance the appearance of a mouth guard by adding color, sparkles, patterns, and textures. One or more fillers can also be included to increase the strength, resilience, texture, or stiffness of the materials. According to this patent, fillers may be added which provide desirable flavors to the mouth guard. The patent states that “it is believed that energy is spread and transferred via the resilient outer region to the interconnected node and fibril structure of the expanded PTFE which absorbs the energy. The strength of the fibrils and their random interconnectedness absorbs the impact by spreading it out to a wider area.” However, the very fact that this mouth guard material is deformable at room temperature by simply biting on it will affect its long term durability, and the relative softness of the material will permit the transmission of forces to the teeth upon high-speed impact of an object.
U.S. Pat. No. 6,491,521 (Dec. 10, 2002) teaches a mouth guard with teeth fashioned from a group of materials, including plastic, plastic composite, rubber, and rubber composite that become formable when heated above normal body temperature of 98.6° F. This mouth guard is pliable and hardens at or below this temperature. The primary purpose of the invention is to solve the need for a mouth guard capable of intimidating opponents in sports by adding the appearance of teeth to the mouth guard. This patent builds upon a number of prior patents, for example U.S. Pat. No. 3,987,546, teaching the method of making a prosthetic denture that includes an assembly of hard acrylic teeth bonded to a semi hard acrylic polymer blend, U.S. Pat. No. 5,951,291 deals with a cosmetic accessory device for teeth that simulates the appearance of teeth and gum.
U.S. Pat. No. 6,491,036 (Dec. 10, 2002) teaches a customizable low-density polyethylene mouth guard with a nucleating agent permitting the softened mouth guard to shrink onto the teeth and guns for a tight fit, and to impart gloss and clarity to the appliance. This patent also teaches the incorporation of antimicrobial agents.